Although vinyl chloride and vinylidene chloride polymers are known to be self-extinguishing and relatively more flame retardant than polymers such as polyethylene and polypropylene, a substantial amount of smoke generally is produced upon the exposure of vinyl chloride or vinylidene chloride polymers to fire. As a consequence, various smoke retardant materials have been added to vinyl chloride polymers and vinylidene chloride polymers to reduce the quantity of smoke produced in the event the polymer is exposed to a flame.
U.S. Pat. No. 4,053,455 teaches the use of amine molybdates as effective smoke retardant additives for vinyl chloride and vinylidene chloride polymers, and suggests the use of melamine molybdate as being preferred since it is white in color, highly effective as a smoke retardant and processes easily without discoloring the polymers. The amine molybdates may be used as the sole smoke retardant, but in some instances are advantageously used in combination with other known smoke retardants. U.S. Pat. No. 4,053,451 describes the use of mixtures of melamine molybdate or substituted melamine molybdates and certain copper compounds as smoke retardants for vinyl chloride polymers and vinylidene chloride polymers. U.S. Pat. No. 4,053,453 discloses the use of copper oxalate with amine molybdates as a smoke retardant mixture.
Amine molybdates may be produced by reacting an amine with a molybdenum compound such as molybdenum trioxide (MoO.sub.3), molybdic acid or a molybdenum salt in an acidic aqueous medium made acidic through the addition of a suitable acid such as an organic acid containing 1 to 12 carbon atoms (exemplified by acetic acid, propionic acid, benzoic acid, and the like) or an inorganic acid (exemplified by hydrochloric acid, nitric acid or sulfuric acid). Excellent results have been obtained using ammonium dimolybdate, ammonium heptamolybdate, sodium molybdate, or commercial "molybdic acid" (which primarily consists of one or more ammonium molybdates) as the molybdenum compound. The preferred reaction method comprises adding an aqueous solution of ammonium molybdate or other molybdenum salt to an acidic solution of the amine. The acidic mixture is refluxed until the reaction is complete, usually for about 1/4 to 4 hours. Alternatively, all of the components of the mixture are charged essentially simultaneously to the reaction vessel followed by refluxing of the mixture until the reaction is completed. The mixture preferably is stirred continuously during the period that reaction is occurring.